1. Technical Field
The present disclosure relates to a method for manufacturing a die assembly and to the die assembly thus obtained.
2. Description of the Related Art
As is known, today so-called MEMS (micro-electromechanical system) sensors are available, an example of which is illustrated in FIG. 1.
In particular, FIG. 1 shows a MEMS sensor 1, which is formed by a package 2, provided inside which are a first die 4, a second die 6, and a third die 8.
The first die 4 forms a so-called sensitive structure 10 of a MEMS type, also known as sensing structure, which comprises one or more elements that are mobile, or in any case deformable, following upon the action of forces that act on the MEMS sensor 1; the sensitive structure 10 is thus designed to generate an electrical sensing signal, which is a function of said forces.
The first die 4 is overlaid by the second die 6, which functions as cap of the sensitive structure 10 and, as such, may not have electrical functions.
In turn, the second die 6 is overlaid by the third die 8 comprising an ASIC (application specific integrated circuit), also known as “read circuit”, which is designed to receive and process the electrical sensing signal so as to generate an output signal. The first and third dice 4, 8 are connected together typically by wire bondings 14 set between pads 16 of the first die 4 and pads 18 of the third die 8.
The first, second, and third dice 4, 6, 8 thus form an assembly 20, which is carried by a supporting layer 22 and is coated with a coating 24, such as, for example, a coating of resin, known as “molding compound”. The supporting layer 22 is delimited by a first surface S1, arranged on top of which is the assembly 20, and by a second surface S2.
On the first surface S1 and, in the case of a package of the so-called “land grid array” (LGA) type, also on the second surface S2 of the supporting layer 22 pads are provided (not illustrated), connected together, for example, by vias or metallizations that extend through the supporting layer 22.
The third die 8 is electrically connected to one or more of the pads provided on the first surface S1, by corresponding wire bondings 26. Consequently, the third die 8 is electrically connected to the pads provided on the second surface S2 and may thus be electrically connected to the outside world.
The assembly 20 is today very widespread since it may be manufactured in a simple and reliable way. For this purpose, in fact, it is possible to bond together a first wafer and a second wafer of semiconductor material, which form, respectively, the first and second dice 4, 6, and singulate the two-wafer structure thus formed so as to form a subassembly including precisely the first and second dice 4, 6. The third die 8, previously singulated, is bonded to the subassembly. However, the assembly 20 has a thickness that is not particularly small given that the operations of bonding between dice require that the latter have thicknesses of not less than (approximately) 100 μm in order to prevent the dice from cracking during the machining steps. Furthermore, the use of dice having small thicknesses entails a degradation of the performance of the sensitive structure on account of a greater sensitivity thereof to the stresses caused by the machining steps, as well as to the stresses that arise during use (for example, thermal stresses).